Electromagnetic transmission devices and electromagnetic transmission systems are used in microwave heating furnaces including microwave reaction furnaces, microwave smelting furnaces, microwave refining furnaces, microwave melting furnaces, microwave blast furnaces, microwave sintering furnaces, and the like, and microwave power transmission systems. For example, in microwave heating and microwave power transmission systems such as experimental devices for space solar power systems, it is required that electromagnetic transmission devices output high-power microwaves. Hence, electron-tube amplifiers such as magnetrons or klystrons characterized by high-power output have been used in microwave transmission devices of these systems for a long time.
Meanwhile, with recent advances in semiconductor amplifier technologies in the fields of radars or telecommunication equipment, progress is being made in developing high-power microwave semiconductor amplifiers that can output, for example, approximately several tens of watts to 200 W in the C-band. Microwave transmission devices such as active phased array antennas (APAAs) equipped with these amplifiers achieve systems that can be enlarged in scale and/or increased in output power.